Bucky, who wasn't truly dead, and his sister watch as Steve greets Clark and welcomes him to the Avengers when he turns eighteen and after he graduates high school. Mary had retired finally. Rosalie graduated early and is a little genius. She is going to be a lab worker in Wakanda. Katie grew up to be a SHIELD agent like Clint.
Mary goes to visit Tony's grave. He really did die in order to defeat Thanos all those years ago. She leaves flowers and she heads to board her flight with Clint.
======
Tokyo, Japan is where Clint and Mary Barton moved to once their kids were grown up. Mary got a job as a tech engineer. Clint grew old and died in Tokyo. Bucky later moves his sister back to Wakanda where she starts her own tech stuff and she ends up, a hundred or so years later, after Rosalie is gone, Clark still lives, Mary moves on and soon becomes Mary Wilson when she marries Sam Wilson, the Falcon.
=====
Sam stands back over five hundred years after the Thanos battle in Tokyo, Japan. His wife wanted to visit Clint's grave and he's totally ok with that. He knows she loved him. He was her first love.
"Hey, Clint," Mary greets. "I hope Katie and Elijah and Rosalie are having fun with you and Laura in Heaven. Clark and I miss you."
Mary's phone rings and it's her son. "Hey, Clark."
"Mom! We need your help!" Clark yells. "There's a robot invasion in New York! The Avengers needs you and Sam back."
"Coming!"
"Work?"
"They need us back," Mary says. "Robot invasion."
"A hero's job never ends."
Mary and Sam share a kiss and they run off to go to America to save New York from cray robots.
